Microscopic performance evaluation of hyperbranched polyamine for sodium montmorillonite hydration inhibition in water-based drilling mud systems

Deep to ultra-deep drilling operations are vital strategies for global energy security, requiring high-performance drilling fluid systems. Water-based drilling fluids/muds (WBDFs/WBDMs), especially clay-containing muds, often degrade under extreme wellbore conditions owing to clay mineral hydration, necessitating advanced inhibition strategies and effective additives to minimize expansion and ensure wellbore stability. Amine-based additives are known for their remarkable inhibitive features. Molecular dynamics simulation was used to evaluate the inhibition performance of a hyperbranched polyamine on sodium montmorillonite (Na-Mnt) hydration in WBDFs. This polyamine demonstrated good solubility and effectively interacts, adsorbs and coats the Na-Mnt surface. Adsorption occurs primarily through H-bonding and electrostatic attractions, with minimal van der Waals (vdW) contributions, forming a protective surface layer/film on the Na-Mnt that modifies its hydrophilic properties by layering the surface. Two adsorption configurations were identified: a stable amine head group and a dimethylamine group. The addition of the polyamine reduced counterion and water mobility, minimizing their coordination as the aqueous NH₄⁺ ions replaced Na ⁺ ions and water molecules, reducing the counterion and Na-Mnt hydration, consequently, weakening the Na-Mnt/water H-bonding network and interaction energy, and thus reducing surface hydration. Temperature had a significant impact on the interaction strength and inhibition performance, while high pressure played a minimal role at elevated temperatures. Overall, the hyperbranched polyamine demonstrated splendid inhibition performance under HT/HP conditions (478 K/75 MPa) for enhancing WBDFs performance and supporting safer, stable and more efficient well drilling works.